Note 9 - Leases (Details Textual)	1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 30, 2024 USD ($)	Dec. 31, 2019 USD ($) ft²	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) ft²	Dec. 31, 2018 USD ($)	Jul. 31, 2019 USD ($)	Jul. 01, 2019 USD ($)	Jun. 30, 2019 USD ($)
Operating Lease, Right-of-Use Asset		$ 1,116,000		$ 1,116,000
Operating Lease, Liability, Total		$ 1,118,000		$ 1,118,000
Operating Lease, Weighted Average Discount Rate, Percent		6.00%		6.00%
Operating Lease, Weighted Average Remaining Lease Term		4 years 109 days		4 years 109 days
Operating Lease, Expense		$ 73,000		$ 147,000
Operating Lease, Right-of-use Asset, Amortization		56,000		111,000
Increase (Decrease) in Operating Lease Liability		$ 55,000		$ 109,000
Lessee, Operating Lease, Renewal Term		5 years		5 years
Asset Retirement Obligation, After Adjustment		$ 555,000		$ 555,000
Gain (Loss) on Change in ARO Estimate				73,000
ARO Original Obligation Amount						$ 704,000
ARO Discount Amount Interest Rate						$ 5.10
Forecast [Member]
Termination of Lease, Penalty	$ 20,000
Accounting Standards Update 2016-02 [Member]
Operating Lease, Right-of-Use Asset							$ 1,200,000
Operating Lease, Liability, Total							$ 1,200,000
Operating Lease, Weighted Average Discount Rate, Percent							6.00%
Maximum [Member]
Operating Lease Arrangement, Maximum Early Termination Penalty		$ 40,000		$ 40,000
Applied Process Engineering Laboratory [Member]
Area of Real Estate Property | ft²		15,000		15,000